Method of making sheet metal turbine bucket



Sept. 11, 1956 G. C. STEINHAUER METHOD OF MAKING SHEET METAL TURBINEBUCKET Filed Aug. 28, 1951 3nventor 5w C'JZ zkkzw Gttornegs UnitedStates 1 METHOD OF MAENG SHEET IVIETAL BUCKET George C. Steinhauer,Danville, Ind., assignor to General Motors Corporation, Detroit, Mich.,a corporation of Delaware Application August 28, 1951, Serial No.243,950

1 Claim. (Cl. 29-1563) This invention relates to blading of a typespecially suited for use in elastic fluid machines such as gas turbineengines and the like, and is directed to an improved construction forand the manufacture of folded sheet metal blades having an integrallyformed foot or base thereon.

The invention is particularly adapted to the manufacture of integrallyfooted blading for use in the rotors of axial flow compressors andturbines. Such blading elements do not admit of simplicity ofmanufacture as they are of complex form, having oppositely curved facesthat may be tapered and/or twisted from the tip to the base of the bladeand may have complicated foot or root structures thereon.

Among the numerous methods proposed for the manufacture of footed bladeshave been various forging, machining, and rolling processes, all ofwhich involve the use of heavy, expensive, and complicated machinery.From the standpoint of simplicity and economy of manu facture theimpeller elements formed in accordance with these processes do notafford the advantages presented by sheet metal blading. Moreover, hollowblades are better adapted to cooling and may be lighter than solidblades.

Several methods for manufacturing sheet metal blades have been proposedheretofore, including that of fabricating a blade from several parts.This method has not been entirely satisfactory in view of the numerousproduction difficulties encountered and the inherent weakness.

of the blades formed in accordance therewith. Another method proposedhas been that of folding a blade blank at the leading edge thereof.Although this method eliminates one or more of the parts, it is not welladapted to the formation of blades of complex shape and meets with theadditional difficulty of unduly stressing the blade material by foldingon a sharp radius at the edge thereof.

Accordingly, it is the general object of the present invention toprovide an improved construction of, and process for the manufacture of,folded sheet metal blades with an integrally formed foot thereon.

Another object is to provide a satisfactory, inexpensive high-productionmethod of manufacturing folded sheet metal blades of low unit cost.

The present invention is directed toward an improved construction of andthe manufacture of a sheet metal blade formed from a single elongatedstrip of metal that is folded back about the central portion thereof ina a recess in the central portion of the blank for the base of theblade, forming the contour curvatures for the blade faces in each end ofthe blank, folding the blank back about the central portion thereof tobring the blade face edge portions thereof together, and uniting theedges of said blank along the forward and trailing edges of the faces ofthe blade.

Among the advantages of the invention is the fact that the curvedsurfaces of the blade and the base thereof are integrally formed from asingle elongated strip of sheet metal stock. Another is the fact thatthe blade is not stressed because it is folded about the base where agenerous radius is available instead of about the leading or trailingedge thereof. A further advantage is that the blade may be readilyformed with complex curved surfaces that may be tapered and twisted.

These and other objects, features and advantages of the invention willappear more fully to those skilled in the art from the followingdetailed description and drawings of the preferred embodiment of theinvention, where- Fig. 1 is an axonometric view of a prepared blank fromwhich the blade is formed;

Fig. 2 illustrates the step of forming the base attachment recess andblade face offset in the blank of Fig. 1;

Fig. 3 illustrates the step of tapering each end of the blank of Fig. 1after the first forming operation;

Fig. 4 illustrates the step of forming the contour curvature of theblade faces including the rough contour of the base attachment;

Fig. 5 is an axonometric view of an insert that is placed in the baseattachment recess prior to folding of the blade about the base thereof;

Fig. 6 is a view along the leading edge of a folded sheet metalcompressor blade constructed in accordance with the invention, and

Fig. 7 is a sectional view taken along the plane 77 of Fig. 6 toillustrate the cross-sectional shape of the blade thereof.

By way of introduction it may be advisable to refer first to Figs. 6 and7 which illustrate a compressor rotor blade which has been constructedin accordance with the process of the invention. The blade 10 comprisesa light hollow blade portion 12 and an integral foot portion 14 which isadapted for mounting in a mating slot in a turbine rotor or the like. Asshown by Fig. 7, the blade portion 12 is of an airfoil form incross-section with one convex side or face 16 and one concave side orface 18. The blade is tapered along its length from the tip 20 to thetop of the foot portion 14 thereof and may also be twisted along itslength, as illustrated. The process of the invention is readily adaptedto the formation of blades of twisted section as will be brought out inthe description of the process of the invention.

The foot portion 14 is of the well-known serrated dovetail or fir-treetype commonly employed for the roots of turbine buckets. The inventioncan, of course, be applied to the formation of other types of bladeroots. A core or filler block 22 is inserted and may be welded or brazedin the base of the blade to reinforce the base and thus facilitatesecuring the base of the blade in its mating slot.

It will be noted that the blade face ofisets 24, 24' are integrallyformed with the blade portions 12 and base portion 14 of the blade,thereby providing a structurally improved blade. Also, the base portionis of continuous unbroken contour formation in the sense that it isnowhere split or interrupted about the base of the blade, a feature thatcontributes substantially to insuring maximum blade strength. Of furtherinterest is the fact that the blade is folded smoothly without creasingon a generous radius about its base, thereby eliminating undesirablestresses occasioned by folding the blade about a Patented Sept. 11, 19563 narrow radius at the leading edge thereof as proposed heretofore.

Turning now to the preferred embodiment of the process of the invention,the blade is formed from a single flat rectangular elongated metal strip26 as illustrated in Fig. l. The base portion 14 of the blade is formedfrom the central portion 28 of the blank between the dotted lines XXindicated thereon While the blade faces are formed from the terminalportions 30, 30' on opposite sides of the central portion of the blank.The blank may be prepared in any of a number of ways known to thoseskilled in the art as by blanking or trimming, for example, from stripor sheet stock. The original stock may be rolled by a hot rollingoperation from a strip or block of metal to the desired thickness of theblank desired. For greater blade strength the grain flow of the metalshould preferably be parallel to the length of the blank.

Fig. illustrates the first forming operation which involv'e's formingthe base attachment or foot section recess 32 in the blank of Fig. l.The extended vertical sections 24, 24' of the recess 32 act as the bladeface oflsets for the base portion 14 of the blade as illustrated in Fig.6. The forming operation may be accomplished in various ways as bypressing the blank of Fig. 1 between suitably formed dies in a hydraulicpress or by striking the blank in a rough die. if desired, the blankingand rough forming operations could be performed simultaneously.

Following the forming operation, the portions 36, 36 of the blank ofFig. 2 are tapered toward the ends as shown in Fig. 3 so as to thickenthe metal in the lower region of the blade portion 12 relative to thethickness at the tip of the blade for purposes of increasing bladestrength. The tapering operation is preferably performed by hot rollingto avoid excessive working of the metal. After the tapering operationthe ends of the blade will be longer than the desired length of thefinished blade.

The next operation, illustrated by Fig. 4, entails forging the contourcurvature of the blade faces in the tape'red portions of the blank ofFig. 3. This step may be accomplished with forging dies having thedesired curvature of the blade faces so that when the ends 38, 30' ofthe blank are brought together, the curved surfaces will mate into anairfoil shape or a dished or crescent shape as required. Any desireddegree of taper or twist may be imparted to the blade faces 'byemployment of appropriately shaped forging dies. The process is thusreadily adapted to the formation of twistedand tapered blades and iscapable of forming such blades with a reasonable degree of accuracy.

The rough serrated contour of the base attachment 32 can be forgedsimultaneously with the forging of the blade face contours with a singleset of forging dies if desired. The bottom of the base attachment andthe diagonal sides thereof are formed from the central flat portionforming a non-corrugated floor 3-4 and the corrugated side portions 36,36, respectively, of the forged recess 32 of the blank of Fig. 4.

The fin or flash (not shown) formed around the edges of the blank ofFig. 4 during the forging operation is then trimmed in a trimming die,for example, and the ends of the blade cut to the desired length. Theblank is then pickled or vapor blasted and inspected.

Prior to the next operation, the tiller block 22 of Fig. 5, which can bea cast metal insert having a shape that conforms to the contour of thebase portion 14 of the finished blade, is inserted in the baseattachment recess of the blank of Fig. 4. The filler block servesseveral purposes including that of facilitating bending of the blank andimproving the rigidity of the base attachment recess and the strength ofthe base portion of the blade.

The next major operation in the formation of the blade is that offolding or bending the blank about the blade attachment recess 32containing the filler block 22 so as to bring the curved blade faceterminal portions thereof and the base portion'weldejd around the fillerinsert 22.

This is followed by grinding of the welds and polishing the bladeportion to obtain the desired edge contour. If ar b se P tion, ma beound 9r t wise accurately finished to the desired base contour. Theblade portion may be restruck for more precise dimensioning.

It will thus be seen that the invention provides a simple andinexpensive construction for an integrally footed blade or bucketelement, the manufacture of which does not require the use ofcomplicated machinery or skilled operators. The invention is not limitedto the particular blade face and foot contours shown and may be readilyapplied within forging limitations to the formation of any shape ofblade.

Although a preferred embodiment of the process of the invention has beendescribed and illustrated, numerous other variations, modifications andapplications within the scope thereof will be apparent to those skilledin the art to which it appertains.

I claim:

A process for forming a turbine bucket comprising an integrally formedblade portion, a planar platform portion, and a substantially triangularshaped foot portion having a fir-tree filler block inserted therein froma fiat, elongated blank of material having an intermediate por-' tionand terminal portions on the opposite sides of the intermediate portionand a triangular filler block hav* ing serrated sides, which methodcomprises the steps of laterally ofisetting the intermediate portion ofthe blank from the plane of the blank to form a recess of uniform depthhaving a pair of spaced parallel walls joining the terminal portions ofthe blank with a floor portion of the recess parallel to the plane ofthe terminal portions, form ing the blade face contour in the terminalportions of the blank and corrugating the floor of said recesstransversely of the blank on each side of a central portion of the floorto form a pair of spaced corrugated portions thefein, placing the saidfiller block on the central portion of the floor of the recess andsmoothly folding the blank about the central portion of the floor of therecess and around the filler block to bring the terminal portions of theblank in face-to face relation to form the said blade portion of thebucket and to bend the said walls of the recess with respect to thecorrugated floor portions to decrease the angle therebetween and thusform the said planar platform portion, and the said base portion, thelatter having serrated sides formed by the spaced corrugated portions'of the floor of the recess, and uniting the adjacent edges of the bladeface terminal portions to form the leading edge and the trailing edge ofthe bucket.

References Cited in the file of this patent UNITED STATES PATENTS412,278 Lee Oct. 3, 1 89 814,804 Raieau Mar. 13, 1906 881,409 Jude Mar.10, 1903 953,568 Westinghouse Mar. 29, 1910 994,166 Kienast Tune 6, l9ll1,530,249 Eveleth a. Mar. 17, 1925 1,829,179 Back on. 27, 1931 1,913,459Skillinan et 1. i June 13,193

(Other refe ences as following page) 5 UNITED STATES PATENTS Smith July9, 1935 Litchfield June 2, 1936 McKee Nov. 11, 1941 Chilton Jan. 9, 19516 Oestrich et a1. July 3, 1951 Atkinson Oct. 7, 1952 Sollinger Oct. 23,1953 FOREIGN PATENTS Germany May 21, 1930

